The deal will give guests at London's Blakes, which charges anywhere between £200 and £1,000 a night, the chance to purchase rooms in the hotel.
GuestInvest will continue to manage the hotel's underlying operations "on a revenue sharing basis" while promoting the rooms to investors.
GuestInvest launched in April 2004, with its prototype hotel the Guesthouse West in Notting Hill.
Two further hotels are currently under development: The 157 room Nest in Bayswater and the 200 room Chiswell Street Hotel in the City of London.
Johnny Sandelson, chief executive officer and founder of GuestInvest, said: "We are delighted to cement this deal and offer Blakes' guests the chance to own a piece of this fabulous hotel.
"We will be making a multi-million pound investment to perfect the hotel services under the guidance of the internationally-renowned interior designer Anouska Hempel, ensuring that the hotel retains its signature design characteristics.
He added that the management team would stay in place with Hempel's husband, the financier Sir Mark Weinberg, joining the GuestInvest board.
Weinberg said: "Our alliance with GuestInvest marks the beginning of an exciting new phase in the long, esteemed history of Blakes. We are bound by confidentiality surrounding this new partnership and are unable to comment further at this time."
By Chris Walton